SciCombinator

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Concept: Artemisinin

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In areas of low malaria transmission, it is currently recommended that a single dose of primaquine (0.75 mg base/kg; 45 mg adult dose) be added to artemisinin combination treatment (ACT) in acute falciparum malaria to block malaria transmission. Review of studies of transmission-blocking activity based on the infectivity of patients or volunteers to anopheline mosquitoes, and of haemolytic toxicity in glucose 6-dehydrogenase (G6PD) deficient subjects, suggests that a lower primaquine dose (0.25 mg base/kg) would be safer and equally effective. This lower dose could be deployed together with ACTs without G6PD testing wherever use of a specific gametocytocide is indicated.

Concepts: Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Anopheles, Apicomplexa, Glucose-6-phosphate dehydrogenase deficiency, Artemisinin

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We present case histories of four patients treated with artemether-lumefantrine for falciparum malaria in UK hospitals in 2015-16. Each subsequently presented with recurrent symptoms and Plasmodium falciparum parasitaemia within 6 weeks of treatment with no intervening travel to malarious countries. Parasite isolates, all of African origin, harboured variants at some candidate resistance loci. No evidence of pfk13-mediated artemisinin resistance was found. Vigilance for signs of unsatisfactory antimalarial efficacy among imported cases of malaria is recommended.

Concepts: Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Anopheles, Quinine, Apicomplexa, Artemisinin

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Background Prevention of reinfection and resurgence is an integral component of the goal to eradicate malaria. However, the adverse effects of malaria resurgences are not known. Methods We assessed the prevalence of Plasmodium falciparum infection among 1819 Mozambican women who delivered infants between 2003 and 2012. We used microscopic and histologic examination and a quantitative polymerase-chain-reaction (qPCR) assay, as well as flow-cytometric analysis of IgG antibody responses against two parasite lines. Results Positive qPCR tests for P. falciparum decreased from 33% in 2003 to 2% in 2010 and increased to 6% in 2012, with antimalarial IgG antibody responses mirroring these trends. Parasite densities in peripheral blood on qPCR assay were higher in 2010-2012 (geometric mean [±SD], 409±1569 genomes per microliter) than in 2003-2005 (44±169 genomes per microliter, P=0.02), as were parasite densities in placental blood on histologic assessment (50±39% of infected erythrocytes vs. 4±6%, P<0.001). The malaria-associated reduction in maternal hemoglobin levels was larger in 2010-2012 (10.1±1.8 g per deciliter in infected women vs. 10.9±1.7 g per deciliter in uninfected women; mean difference, -0.82 g per deciliter; 95% confidence interval [CI], -1.39 to -0.25) than in 2003-2005 (10.5±1.1 g per deciliter vs. 10.6±1.5 g per deciliter; difference, -0.12 g per deciliter; 95% CI, -0.67 to 0.43), as was the reduction in birth weight (2863±440 g in women with past or chronic infections vs. 3070±482 g in uninfected women in 2010-2012; mean difference, -164.5 g; 95% CI, -289.7 to -39.4; and 2994±487 g vs. 3117±455 g in 2003-2005; difference, -44.8 g; 95% CI, -139.1 to 49.5). Conclusions Antimalarial antibodies were reduced and the adverse consequences of P. falciparum infections were increased in pregnant women after 5 years of a decline in the prevalence of malaria. (Funded by Malaria Eradication Scientific Alliance and others.).

Concepts: Immune system, Antibody, Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Quinine, Artemisinin

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KEY MESSAGE : Rooting of Artemisia annua increases trichome size on leaves and helps drive the final steps of the biosynthesis of the sesquiterpene antimalarial drug, artemisinin. Artemisia annua produces the antimalarial drug, artemisinin (AN), which is synthesized and stored in glandular trichomes (GLTs). In vitro-grown A. annua shoots produce more AN when they form roots. This may be a function not of the roots, but rather media components such as the phytohormones, α-naphthaleneacetic acid (NAA) and 6-benzylaminopurine (BAP), or salts and sucrose used to maintain either rooted or unrooted shoot cultures. We investigated how three main media components altered artemisinic metabolite production, pathway gene transcripts, and GLT formation in both mature and developing leaves in rooted and unrooted cultures. Although transcript levels of AN biosynthetic genes were not altered, AN levels were significantly different, and there were major differences in both artemisinic metabolite levels and trichomes in mature versus developing leaves. For example, NAA induced higher AN production in rooted shoots, but only in mature leaves. In developing leaves, BAP increased GLT density on the leaf surface. When both phytohormones were present, GLTs were larger on young developing leaves, but smaller on mature leaves. Furthermore, although other media components increased GLT density, their size decreased on young leaves, but there was no effect on mature leaves. Roots also appeared to drive conversion of artemisinic precursors towards end products. These results suggest that, while the presence of roots affects AN and trichome production, phytohormones and other media constituents used for in vitro culture of A. annua also exert an influence.

Concepts: Gene, Amino acid, Artemisinin, Leaf, Plant morphology, Antimalarial drug, Artemisia annua, Trichome

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The discovery of new chemical starting points with the ability to inhibit Plasmodium falciparum sexual stages, and therefore block the disease transmission, is urgently required. These will form the basis for the development of new therapeutic combinations for the treatment and elimination of malaria and the ultimate goal of global eradication. Recent screening of large chemical libraries against the parasite asexual stages has resulted in the public availability of focused subsets of known antimalarial actives, which represent an excellent starting point for the identification of new gametocytocidal compounds. New stage-specific methodologies aimed at increasing the throughput for assessing compound activity against in vitro cultured gametocytes have recently been published. This article discusses the challenges of assay-oriented large-scale gametocyte culturing and reviews the state-of-the art in gametocytocidal assay development and outcomes.

Concepts: Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Anopheles, Quinine, Artemisinin, Gametocyte

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Background. Artemisinin-based combination therapy (ACT) is very effective in clearing asexual stages of malaria and reduces gametocytemia, but may not affect mature gametocytes. Primaquine is the only commercially available drug that eliminates mature gametocytes.Methods and objectives. We conducted a two-arm open-label randomized controlled trial to evaluate the efficacy of single dose primaquine (0.75 mg/kg) following treatment with dihydroartemisinin-piperaquine on P. falciparum’s gametocytemia, in Indonesia. Patients with symptomatic uncomplicated falciparum malaria, normal glucose-6-phosphate dehydrogenase (G6PD) enzyme levels, aged ≥5 years and hemoglobin levels ≥8 g/dL were assigned by computerized-generating sequence to receive either a standard 3-day course dihydroartemisinin-piperaquine alone (n=178) or combined with a single dose of primaquine on Day-3 (n=171). Patients were seen on days 1, 2, 3, 7 and then weekly for 42 days to assess the presence of gametocytes and asexual parasites by microscopy. Survival analysis was stratified by the presence of gametocytes on Day-3.Results. DHP prevented development of gametocytes in 277 patients without gametocytes on Day-3. In the gametocytemic patients (n=72), primaquine was associated with faster clearance of gametocytes (HR=2.42, 95% CI 1.39- 4.19, P= 0.002) and reduced gametocyte densities (geometric mean area-under-the-curve 157 vs 330, P= 0.018). The Day-42 cure rate of asexual stages in the DHP-PQ and DHP-alone arms were: PCR-unadjusted: 98.7% vs 99.4% respectively; PCR-adjusted:100% for both. Primaquine was well tolerated.Conclusion. Addition of a single dose of primaquine shortens the infectivity period of DHP treated patients with acute uncomplicated malaria and should be considered in low transmission regions that aim to control and ultimately eliminate falciparum malaria.Clinical Trial Registration. NCT01392014.

Concepts: Pharmacology, Malaria, Plasmodium falciparum, Plasmodium, Randomized controlled trial, Plasmodium vivax, Glucose-6-phosphate dehydrogenase deficiency, Artemisinin

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Background. Plasmodium knowlesi commonly causes severe malaria in Malaysian Borneo, with high case-fatality rates reported. We compared risk and spectrum of severe disease from P.knowlesi, P.falciparum and P.vivax and outcomes following introduction of protocols for early referral and intravenous artesunate for all severe malaria.Methods. From September 2010-October 2011 we prospectively assessed non-pregnant patients ≥12 years-old admitted to Queen Elizabeth Hospital (QEH), Sabah, with PCR-confirmed Plasmodium monoinfection. Standardized referral (4+ parasite-density and/or any severity-criterion) and pre-referral intravenous artesunate were instituted at district hospitals.Results. Severe malaria (modified-WHO 2010 criteria) occurred in 38/130 (29%) patients with P.knowlesi, 13/122 (11%) with P.falciparum and 7/43 (16%) with P.vivax. Most common severity criteria in knowlesi malaria included parasitemia>100,000/µL (n=18), jaundice (n=20), respiratory distress (n=14), hypotension (n=13), and acute kidney injury (n=9). On multivariate analysis, P. knowlesi was associated with a 2.96 (95%CI:1.19-7.38)-fold greater risk of severity than P. falciparum (p=0.020); only parasitemia and schizontemia >10%, but not age, independently predicted knowlesi severity. Risk of severe knowlesi malaria increased 11-fold with parasitemia >20,000/µL, and 28-fold with parasitemia >100,000/µL. Nearly all (92%) knowlesi malaria patients received oral artemisinin-therapy; 36/38 (95%) and 39/92 (42%) with severe and non-severe disease also received ≥1 dose of intravenous artesunate. For all species, median parasite clearance-time was two days and no deaths occurred.Conclusions. P.knowlesi is the commonest cause of severe malaria at QEH, with parasitemia the major risk-factor for severity. Early referral and treatment with artesunate was highly effective for severe malaria from all species and associated with zero mortality.

Concepts: Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Anopheles, Apicomplexa, Artemisinin, Plasmodium knowlesi

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Successful control of falciparum malaria depends greatly on treatment with artemisinin combination therapies. Thus, reports that resistance to artemisinins (ARTs) has emerged, and that the prevalence of this resistance is increasing, are alarming. ART resistance has recently been linked to mutations in the K13 propeller protein. We undertook a detailed kinetic analysis of the drug responses of K13 wild-type and mutant isolates of Plasmodium falciparum sourced from a region in Cambodia (Pailin). We demonstrate that ART treatment induces growth retardation and an accumulation of ubiquitinated proteins, indicative of a cellular stress response that engages the ubiquitin/proteasome system. We show that resistant parasites exhibit lower levels of ubiquitinated proteins and delayed onset of cell death, indicating an enhanced cell stress response. We found that the stress response can be targeted by inhibiting the proteasome. Accordingly, clinically used proteasome inhibitors strongly synergize ART activity against both sensitive and resistant parasites, including isogenic lines expressing mutant or wild-type K13. Synergy is also observed against Plasmodium berghei in vivo. We developed a detailed model of parasite responses that enables us to infer, for the first time, in vivo parasite clearance profiles from in vitro assessments of ART sensitivity. We provide evidence that the clinical marker of resistance (delayed parasite clearance) is an indirect measure of drug efficacy because of the persistence of unviable parasites with unchanged morphology in the circulation, and we suggest alternative approaches for the direct measurement of viability. Our model predicts that extending current three-day ART treatment courses to four days, or splitting the doses, will efficiently clear resistant parasite infections. This work provides a rationale for improving the detection of ART resistance in the field and for treatment strategies that can be employed in areas with ART resistance.

Concepts: Immune system, Gene, Malaria, Plasmodium falciparum, Plasmodium, Apicomplexa, In vivo, Artemisinin

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Resistance by Plasmodium falciparum to almost all clinically used antimalarial drugs requires the development of new classes of antimalarials. 6-Iodouridine (15), a novel and potent inhibitor of orotidine-5'-monophosphate decarboxylase (ODCase), exhibited efficacy in a mouse model infected by P. chabaudi chabaudi. Compound 15 exhibited promising antimalarial activity against P. falciparum, including drug-resistant isolates, and no rapid drug-resistant populations of the parasite were observed when challenged with 15. Uridine provided options to overcome any toxicity in the host but still suppressing the parasite load when treated with 15. In drug combination studies, compound 15 showed good efficacy in vivo with artemisinin and azithromycin. The propionyl ester of 15 exhibited superior antimalarial efficacy. Antimalarial activities of 15, its prodrugs and potential for combination therapy are discussed in the context of novel strategies.

Concepts: Pharmacology, Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Quinine, Artemisinin, Antimalarial drug

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Background KAF156 belongs to a new class of antimalarial agents (imidazolopiperazines), with activity against asexual and sexual blood stages and the preerythrocytic liver stages of malarial parasites. Methods We conducted a phase 2, open-label, two-part study at five centers in Thailand and Vietnam to assess the antimalarial efficacy, safety, and pharmacokinetic profile of KAF156 in adults with acute Plasmodium vivax or P. falciparum malaria. Assessment of parasite clearance rates in cohorts of patients with vivax or falciparum malaria who were treated with multiple doses (400 mg once daily for 3 days) was followed by assessment of the cure rate at 28 days in a separate cohort of patients with falciparum malaria who received a single dose (800 mg). Results Median parasite clearance times were 45 hours (interquartile range, 42 to 48) in 10 patients with falciparum malaria and 24 hours (interquartile range, 20 to 30) in 10 patients with vivax malaria after treatment with the multiple-dose regimen and 49 hours (interquartile range, 42 to 54) in 21 patients with falciparum malaria after treatment with the single dose. Among the 21 patients who received the single dose and were followed for 28 days, 1 had reinfection and 7 had recrudescent infections (cure rate, 67%; 95% credible interval, 46 to 84). The mean (±SD) KAF156 terminal elimination half-life was 44.1±8.9 hours. There were no serious adverse events in this small study. The most common adverse events included sinus bradycardia, thrombocytopenia, hypokalemia, anemia, and hyperbilirubinemia. Vomiting of grade 2 or higher occurred in 2 patients, 1 of whom discontinued treatment because of repeated vomiting after receiving the single 800-mg dose. More adverse events were reported in the single-dose cohort, which had longer follow-up, than in the multiple-dose cohorts. Conclusions KAF156 showed antimalarial activity without evident safety concerns in a small number of adults with uncomplicated P. vivax or P. falciparum malaria. (Funded by Novartis and others; ClinicalTrials.gov number, NCT01753323 .).

Concepts: Malaria, Plasmodium falciparum, Plasmodium, Plasmodium vivax, Anopheles, Quinine, Artemisinin, Mefloquine